Currently, power supply control apparatuses (e.g., see JP 2010-239835A) that, by turning a switch provided on an electrical wire connecting a battery and a load such as a motor, for example, on/off, control power supply from the battery to the load via the electrical wire have been proposed.
The power supply control apparatus described in JP 2010-239835A receives input of a signal instructing to start or end power supply to the load. The power supply control apparatus described in JP 2010-239835A turns the switch on/off in accordance with the contents indicated by the input signal, and calculates the temperature difference between the ambient temperature of the electrical wire and the electrical wire temperature in time series, based on the value of current flowing through the electrical wire.
This temperature difference is calculated based on a previous temperature difference calculated previously and the value of current flowing through the electrical wire. In the case where the electrical wire temperature calculated by adding the ambient temperature to the calculated temperature difference is greater than or equal to a predetermined temperature, the switch is turned off regardless of the contents of the input signal. Power supply via the electrical wire thereby stops and the electrical wire temperature falls, thus avoiding any risk of smoke being generated or fire starting from the electrical wire.
Also, the power supply control apparatus described in Patent Document suspends time-series calculation of the temperature difference and suppresses power consumption, in the case where the calculated temperature difference is approximately zero, in a state in which the switch is off due to a signal instructing to end power supply having been input.
In the initial calculation after time-series calculation of the temperature difference is resumed, an initial temperature difference to be used as the previous temperature difference is set to zero.
However, the power supply control apparatus described in JP 2010-239835A does not suspend time-series calculation of the temperature difference until the calculated temperature difference is approximately zero. Thus, with the power supply control apparatus described in JP 2010-239835A, there is a problem in that power consumption remains large, due to the short period for which time-series calculation of the temperature difference is suspended.
As a configuration that solves this problem, the power supply control apparatus described in JP 2010-239835A could conceivably be configured to suspend time-series calculation of the temperature difference regardless of the calculated temperature difference.
However, with this configuration, time-series calculation of the temperature difference could possibly be resumed in a state in which the actual temperature difference between the electrical wire temperature and the ambient temperature is high. In this case, since the initial temperature difference is set to zero, an inappropriate temperature difference smaller than the actual temperature difference is calculated. Accordingly, since the calculated electrical wire temperature is lower than the actual electrical wire temperature, there is a risk that power supply will not be stopped, despite the actual electrical wire temperature being a temperature at which power supply via the electrical wire should be stopped in order to prevent the electrical wire temperature from rising.
The present invention was made in view of the above situation, and an object of the invention is to provide a power supply control apparatus that is able to reduce power consumption and to appropriately calculate the temperature difference between the ambient temperature of an electrical wire and the electrical wire temperature.